We aim to understand aspects of macromolecular assembly and its control, by combining structural and biochemical studies of viruses, viral membrane proteins, and membrane-associated cytoskeletal proteins such as clathrin. This proposal focuses on electron microscopic investigations of clathrin-cage formation, of intermediates in spherical-virus assembly, of surface organization of viral membranes, and of membrane-fusion mechanisms. (1) We will study the structure of in vitro assembled clathrin cages by computer-assisted image analysis of negatively-stained specimens, in an effort to understand the precise relationship of the pinwheel-like clathrin trimer to the assembled cage. (2) We will dissect the in vitro reassembly pathway of turnip crinkle virus, for which the structure is known at 3 Angstrom resolution, using a combination of physical biochemistry and electron microscopy to assay intermediate stages. (3) We will combine electron microscopy with molecular model building to understand the packing of influenza haemagglutinin and neuramindase in the viral membrane. (Both proteins are being studied by high resolution x-ray crystallography.) (4) We will prepare and examine two-dimensional arrays of viral glycoproteins in lipid bilayers (Sindbis, influenza) for evidence of lattice rearrangements postulated to have an important role in membrane fusion. Electon microscopic and powder x-ray diffraction studies of these arrays will be carried to as high a resolution as possible.